Al-based alloys and Cu-based alloys have widely been used, for the reasons of their having low electric resistivity and high processability, in the field of flat panel displays (FPDs) such as liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescence displays (ELDs), and filed emission displays (FEDs). More specifically, Al-based alloys and Cu-based alloys have been used for interconnection layers, electrode layers, reflective electrode layers, and other materials.
For example, active matrix-type liquid crystal displays each have thin-film transistors (TFTs) as switching elements, pixel electrodes formed from conductive oxide layers, and a TFT substrate having interconnection lines which include scan lines and signal lines. The scan lines and signal lines are electrically connected to the pixel electrodes. For interconnection materials forming scan lines and signal lines, there have widely been used pure Al thin films or various Al-based alloy thin films such as made of Al—Nd alloys, or pure Cu thin films or various Cu-based alloy thin films such as made of Cu—Mn alloys.
For the formation of Al-based alloy thin films or Cu-based alloy thin films, a sputtering method using a sputtering target has widely been used. In the sputtering method, a plasma discharge is first formed between a substrate and a sputtering target made of a material (target material) having the same composition as that of a thin film material. A gas ionized by the plasma discharge is then impinged on the target material to beat out the atoms of the target material and these atoms are deposited onto the substrate to form a thin film. Unlike a vacuum vapor deposition method or an arc ion plating method, the sputtering method has a merit that it can form a thin film having the same composition as that of a target material. In particular, Al-based alloy thin films or Cu-based alloy thin films, which are formed by the sputtering method, can provide a solid solution of alloy elements which are not made into a solid solution under the equilibrium state, and can exhibit excellent performance as thin films. Therefore, it is an industrially effective method of forming a thin film, and the development of a sputtering target as its material has been promoted.
In recent years, for making a response to an improvement in the productivity of FPDs and other requirements, film-formation rate in the sputtering step has a tendency to be made higher than the conventional one. Increasing sputtering power is the simplest way to make film-formation rate higher. However, if increasing sputtering power, sputtering failures such as splashes (fine melted particles) may occur to cause defects in interconnection thin films or the like, which leads to adverse effects such as a decrease in the yield and performance of FPDs.
Thus, for the purpose of preventing the occurrence of sputtering failures, for example, the methods described in patent documents 1 to 4 have been proposed. Among them, all of patent documents 1 to 3 have been made on the basis of the viewpoint that the occurrence of splashes is attributed to fine voids in the texture of a target material. The occurrence of splashes is prevented by controlling the dispersion state of particles of a compound between Al and a rare earth element in the Al matrix (patent document 1), controlling the dispersion state of a compound between Al and a transition element in the Al matrix (patent document 2), or controlling the dispersion state of an intermetallic compound between Al and an added element in the target (patent document 3). Patent document 4 discloses a technique to inhibit the occurrence of surface defects associated with machine processing and to reduce arcing which may occur in the sputtering, by adjusting the hardness of a sputter surface, followed by finish machine processing.
Furthermore, patent document 5 describes a method of carrying out sputtering at a high film-formation rate by controlling the ratio of crystal orientations on the sputter surface of a sputtering target. It is described therein that if the content ratio of crystal orientation <111> when the sputtering surface is observed by an X-ray diffraction method is increased to 20% or higher, the ratio of target substances flying in the direction normal to the sputtering surface is increased to make film-formation rate higher. In the section of Examples, the results are described, which were obtained by the use of an Al-based alloy target containing 1 mass % of Si and 0.5 mass % of Cu.
Also, patent document 6 has no explicit description of film-formation rate, but describes that to extend the electromigration lifetime of interconnection lines and improve the reliability of interconnection lines, the content ratio of crystal orientation <200> when the sputtering surface is observed by an X-ray diffraction method may be increased to 20% or higher. In the section of Examples, the results are described, which were obtained by the use of an Al-based alloy target containing 1 mass % of Si and 0.5 mass % of Cu.
On the other hand, the applicant of this application mainly discloses a technique to inhibit arcing which becomes a problem when film-formation rate is made higher (patent document 7). Patent document 7 is directed to an Al—Ni-rare earth element alloy sputtering target, and suggests that if the area ratio of specific crystal orientations is controlled, arcing can sufficiently be inhibited.